Veterinary drugs benzimidazole anthelmintics

The discovery of parbendazole stimulated a vigorous search for better benzimidazole anthelmintics in different pharmaceutical companies of the world. Soon a number of drugs (14-22) were introduced in veterinary and humans medicine. All these benzimidazole anthelmintics may be regarded as the 5(6)-derivatives of car-bendazim (10) which per se is an effective pesticide rather than an anthelmintic [12]. A novel non-carbamate benzimidazole fasciolicide, triclabendazole (23) [13] and a benzimidazole-2-carbamate anthelmintic, ricobendazole (24) [14] have been introduced recently (Table 1). 

Thiabendazole. This benzimidazole derivative (12) is an effective oral drug used in the treatment of intestinal roundworms and selected tissue parasites. Infections with S. stercorahs are commonly treated with thiabendazole for two days. Disseminated strongyloidiasis is treated for at least five days. Satisfactory results have been reported when used for T. spirahs infections however, its effectiveness on encapsulated muscle larvae has not been clinically demonstrated. Extensively used in veterinary medicine, thiabendazole was the first broad-spectrum benzimidazole anthelmintic. It is widely used in the United States. The mechanism of action is not clearly understood, but it has been shown that thiabendazole inhibits the enzyme fiima.ra.te reductase, which is found specifically in the mitochondria of helminths (31). 

Veterinary anthelmintics. Among the most used drugs are pyrantel 6.38) the organic phosphates [such as metrifonate 6,28) and dichlorvos 13,29) and the benzimidazoles, particularly thiabendazole 6,36) which has a wide range of activity against both adult and immature worms in cattle, horses, pigs, and sheep. It is so selective, and so rapidly eliminated, that animals can safely be slaughtered, and milk from cows used, soon after administration. 

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